As internal combustion engines have advanced with fuel injection systems and the like, their power density has increased, providing more horsepower with smaller size engine blocks, shafts, and bearings. This has put increased burdens on the clutches that must start up and connect the engines to the driven load. Moreover, clutches must often absorb more energy in starting large loads.
The traditional flywheel-mounted pilot bearings that have helped support the clutch output shaft have proven problematic to engine life as the reaction loads exceed the capacity of the engine bearings. There is a need to provide engine clutches with output shafts that are independent of the engine bearings. In addition, there is a need for an engine clutch that is axially short to minimize the overall length of the drive system. Thus, the extra length necessary to accommodate a double bearing-supported output shaft necessitates improved clutch architecture to maintain or reduce the overall length.
It is now commonplace for manufacturers of engine powered equipment to use the same engine for multiple applications, some of which are directly coupled to the driven equipment, while others are belt driven. Prior art clutches have required different shaft bearing arrangements for direct and belt drives, thus requiring the equipment manufacture to stock and support two different clutch models. There is a need for engine clutches to be designed with a bearing arrangement that can provide long, trouble-free life in both direct coupled and belt drive applications.
Previously known fluid-actuated engine clutches have been typically offered in three piston configurations. The first includes rotary piston designs with rotary unions at the output shaft end. These clutches require rifle drilled shafts, and the rotary unions add length and complexity. Moreover, such configurations are not adaptable to direct drive applications. Rotary piston designs with rotary seals that fit around the shaft have also been provided. Again, these designs require rifle drilling of the shafts. Moreover, the seals are expensive, especially in larger diameter shafts, and they add considerable length to the overall assembly. Finally, stationary piston clutches have been provided with separate bearings to transfer the thrust loads from the piston to the clutch and to restrain the reaction loads. Typically, the output shaft in these designs used two bearings, for a total of four bearings and considerable axial length. In the past, large hydraulically actuated engine clutches have often used oil cooling of the friction disk pack to extend life, especially where high energy start-up is required. This oil flow can also extend the life of the bearings. Prior art clutches commonly required oil flow through the shaft in order for the oil to effectively reach the friction disks and bearings. This again added to overall length, size, and cost of manufacture.
Finally, previously known fluid-actuated clutch assemblies, particularly those operating with high inertia equipment, such as tub grinders, horizontal grinders, rock crushers and the like, have been shown to be more efficient and safe when an output shaft brake is included with the clutch. However, in the past such output shaft brakes have been complex, expensive, and given to increasing the overall size of the clutch with which it is used.